A piston of this kind is described and illustrated in DD-PS 73 453. In this known embodiment the filler piece is tapered in steps towards its inner end, and the tapered section has an external thread with which the filler piece is screwed into a complementary internal thread in the wall of the cavity in the hollow body and is thus secured. To prevent unscrewing, a pin parallel to the axis is arranged at the free end of the hollow body and of the filler piece in a position in which it passes through the interface between the filler body and the hollow body. The locking pin is secured axially by a radial lock washer, inserted in an annular groove at the free end of the cavity, and a plate spring, inserted between the lock washer and the filler piece, whose dimensions are such that its peripheral edge extends in front of the facing end of the locking pin. The locking pin can thus not move axially out of its receiving hole.
This known embodiment is very complicated and expensive, not only because an external and internal thread and the receiving hole for the locking pin have to be provided but also because the locking pin must be fitted. Furthermore the axial securing of the filler piece is inadequate, because owing to the different materials and thermal coefficients of expansion of the hollow body and of the filler piece, the fluctuations in temperature to be expected in operation of the piston machine loosen the thread, although the filler piece is prevented from unscrewing axially by the locking pin.